I know people come searching here for organic pest control methods, and I occasionally mention a few specific techniques, but mostly I talk about a far more important concept that pretty much gets rid of pests altogether.

I don't read very many organic gardening blogs. I find I pick up more useful gardening tips from reading organic farming research and organic gardening books.

Most blogs just seem to be covering gardening topics that I'm not really interested in, which is fine - I tend to lean slightly towards the ecological side of gardening rather than the aesthetic side, and to advanced soil building and food growing techniques rather than the basics.

My rainwater barrel is super cool and a good metaphor for water conservation. But I find it interesting to actually run the math and see how little water they hold, and I wonder if they are taking the limelight away from more important organic gardening practices.

Rainwater Barrel Mathematics 101

If your roof is 1000 square feet (100 square meters) and you get 1 inch of rain on a spring Friday afternoon (don’t worry, it had to get it out of its system before the sunny, warm weekend ahead), you will have 625 gallons of water coming off that roof.

I don’t know about where you live, but where I live, 1 inch of rain is common.

Let’s say you are rain harvesting into a 60 gallon rainwater barrel that will get nice and full and you can use it when organic gardening to water your tomatoes another day. But 90% of that water is going elsewhere, maybe into your city’s sewer system. Your barrel can only take 1/10 inch of rain from that 1000 square foot roof.

So while I like the 60 gallon rainwater barrel, I think there are better solutions.

Rain Harvesting Into Cisterns

A 600 gallon rainwater cistern could handle almost a full inch and a 1500 gallon cistern could easily take 2 inches. Think of it as a giant rainwater barrel. I think every house should have one of these, the size dependant on the amount of rainfall in your area.

They can be a bit tricky to fit into the landscape and some people think they are an eyesore, but they can be cleverly hidden or even buried.

Rain Harvesting Into Ponds

A more attractive organic gardening solution for rain harvesting would be to build a small pond to catch the water. A pond the size of a king size bed and 2 feet deep would hold your inch of water and if constructed thoughtfully, would provide drinking water for insects and animals.

This awesome pond holds way more water than a rainwater barrel

Every organic garden should have some open water in it for this purpose. Mosquitoes aren’t a problem if you keep the water moving and put some effective microorganisms in it, but that’s for another article.

While your rain harvesting into a pond, you might as well bring your greywater into it to be cleaned and used as well, rather than piping it to the sewer or septic system. Your sink, shower and laundry water can all be put to use in the garden. Make sure to use non-toxic soaps, shampoos and detergents.

Rain Harvesting Into Soil

What I think we should mostly be focusing on is the soil in our organic gardens. The soil is the best way to hold onto water and makes rain harvesting into a rainwater barrel look like child’s play (not that there’s anything wrong with child’s play).

Let's look at how it works using 1 inch of rain as an example. If your roof is 1000 square feet (100 square metres) and you get 1 inch of rain, you will have 625 gallons of water coming off that roof.

A loamy sand, which is 70-85% sand (hence not very good at holding water), can hold 1.1 to 1.2 inches of “plant available water” (plant available water refers to the water that can actually be taken up by plant and microbes and also lost to evaporation; the soil can hold more water than that, but some of it is so tightly held by the soil that it can’t be used).

This loamy sand will already be fairly saturated from our 1 inch rain, though, so it won’t take much of the water from the roof.

A silt loam, which is 75-90% silt, is great at rain harvesting as it can hold the most “plant available water” at 2 to 2.5 inches. It can handle all of the 1 inch rain if you can spread the roof runoff over 1000 square feet. That might be possible with some smart engineering.

A clay soil, which has at least 55% clay, actually holds less plant available water than the silt loam because while it can hold more water, it is held so tightly that plants and microbes can’t get it. It holds 1.2 to 1.5 inches of water, again not much of our roof runoff.

So what to do?

Organic Matter: The Magic Ingredient

There is one thing that we can put in and on our soil that will hold the extra water, and that is organic matter. Organic matter is a rain harvesting genius. I don’t know exactly how much water organic matter can hold, but an article on the USDA website says it can hold 10 to 1000 times more water and nutrients than the same amount of soil minerals.

Even if organic matter holds only 4 times its weight in water, you can hold nearly an extra inch of water if you can increase the organic matter content of your soil by 1.5%, easily doable.

Rain harvesting into the soil is the best option

A study in the Journal of Soil and Water Conservation found that regardless of the type of soil (sandy loam, clay, etc.), “as organic matter increased from 1 to 3%, the available water capacity approximately doubled. When organic matter content increased to 4%, it then accounted for more than 60% of total.”

That means we can now be rain harvesting 2 or 3 inches of rain from the roof, 20-30 times more than your rainwater barrel. This is what organic gardening is all about.

Organic matter can be brought in via compost or mulch. Incorporating 2 inches of good compost into the top 12” of a new garden bed will easily increase the organic matter content by 2-3% (although you might as well go for 6 inches of compost while you’re doing it).

Mulch goes on top of the soil, but it too holds a lot of water.

Now all that’s left is to direct the runoff to your gardens with gutters, and perhaps slight grading of the ground and swales and berms.

Rain Harvesting Summary

The rainwater barrels are a nice idea, but they don’t go very far in rain harvesting from the roof. Cisterns and ponds can hold more and should be used, but the winner in this event is the soil and especially organic matter.

Most soils are low in organic matter and if that’s the case for yours, bringing in lots of compost and mulch will transform your soil into the ultimate storage tank.

There are many mulch types available for your organic garden, but which is the best mulch for you?

This article explores some of the most popular types of mulch and ultimately comes to a conclusion with what you should use.

What is mulch? It's really anything that we put on the soil surface to cover the ground.

Landscaping Fabric - Not The Best Mulch

Landscaping fabric is considered part of our mulch because it is often placed on the soil under various types of mulch in order to help control weeds. The cheap stuff doesn’t work very well, but thicker fabric can work for awhile before weeds start to find their way through the cracks or just start on top of the mulch.

Unfortunately, that thick landscaping fabric can also stop water from getting down to the soil, especially on a slope where the water just slides down the fabric to the bottom. It doesn’t take long for the landscape to show signs of suffering in this case.

But the biggest problem with this fabric is that it doesn’t allow organic matter to recycle into the soil. When you put landscaping fabric on, it means your soil doesn’t get to eat anymore. This is definitely not the best mulch for organic gardening purposes.

Soil needs to be consistently replenished with organic matter, so any of the mulch types we choose have to be composed of organic matter.

Soil is replenished in nature and in our gardens when leaves fall in autumn, and since many of our gardens are low in organic matter anyway, it also happens when we intentionally bring in more leaves, straw, compost and other organic matter to improve the soil.

Putting landscaping fabric in the garden stops all of this and slowly kills the fertility and structure of the soil, and everything living in it. The only potential use is on pathways, since we are compacting them anyway and not trying to increase the organic matter. But we need to look elsewhere for the best mulch.

Why Organic Matter Is One Of The Better Types Of Mulch

When it comes to choosing a good mulch, we need to think, what is mulch for?

Weeds. A continuous thick, dense layer of 2”-4” of one of the best mulch types is one of my favorite ways to control weeds because not only does it smother most of them out, it makes the ones that do find their way through so much easier to pull, especially if you have been clever enough to regularly hit the garden (and the mulch) with some water.

Weed seeds will always be floating in, but a thick mulch will stop them

We have other organic gardening chores to do, so eliminating most of the weeds is a good goal. It may be necessary to kill some tap-rooted or perennial weeds before placing the mulch on top of them.

In addition, maintaining a dense, multi-layer plant cover on your soil consisting of a groundcover below and flowers, shrubs and trees above will stop most weeds from growing.

But the reason organic matter is that best mulch is that it provides a huge number of benefits to your garden. In fact, t is one of the most important things you can do. If you use an appropriate kind of mulch (we'll get to what is "appropriate" soon), here are the other main benefits:

Soil Health. The best mulch types are persistently and continuously working to improve the health of the soil. They are being broken down by microbes and increasing the organic matter content of the soil.

Organic matter is an incredibly important part of the soil. It improves soil structure, and as it is broken down, its nutrients are releasing into the soil, making it one of the only types of mulch that improves fertility. It prevents compaction from us walking in the garden and erosion from the wind or gravity on steep slopes. It also moderates the soil temperature, which is good for anything (plant, animal and microbe) living there.

Water. Organic matter is the best mulch because it is broken down into humus, which has an incredible ability to hold onto lots of water. But even before it is broken down, mulch holds a lot of water on its own and allows it to more slowly infiltrate into the soil.

It also reduces compaction (and leaching of nutrients) caused by a heavy rain, and erosion that happens when a lot of rain falls and there is runoff. Conversely, when the sun is shining, it also prevents evaporation from the soil surface.

So the best mulch actually improves the biodiversity of your entire soil ecosystem by giving all manner of critters a place to live, food to eat and water to drink. It even looks good in the organic garden if one of the right types of mulch is used.

So what is the best mulch? Well, it has to satisfy all of the conditions in the above article, so we can probably figure it out by a process of elimination. Let's start with mulches that satisfy very few of our conditions and get rid of them right away:

1. Stones or gravel provide some of the benefits in that they protect the soil from erosion and decrease evaporation, but they do not breakdown and so do not do much to improve soil health. They are not one of the best mulch types.

2. Bark mulch and wood chips are some of the most commonly used mulching materials in the garden. They have some benefits and some potential downsides. They do most of the above things well, but unfortunately, they have a couple of issues making them one of the types of mulch I don't tend to use.

Bark mulch and wood chips are not the best mulch types

The first is that they are very high in carbon and very low in nitrogen. This means that the beneficial microbes in the soil may pull all of the available nitrogen from the surrounding area in order to be able to eat the wood, which often ends up causing a nitrogen deficiency in your soil and plants.

This is more of an issue when you incorporate the mulch into the soil, and doesn't seem to cause as big of a problem when the mulch is left on top.

Bark in particular is low in nutrients (so it doesn't improve soil fertility) and often high in toxins (it’s a tree’s first line of defense against pests), so it causes toxicity problems in the soil. It even contains oils that repel water, rather than more appropriate mulch materials that will hold onto water.

Wood chips are a little better, but there is another mulch coming up soon that is more in line with nature.

Twigs and small branches, on the other hand, have been shown to be much more beneficial that wood chips. They contain more nutrition and don't cause the nitrogen deficiency problems either.

3. Straw and Hay are not the most aesthetically pleasing, but they are fairly good types of mulch. They're used in organic gardening, but the main issue for most people will be that they're not always easy to find and they break down so quickly that they have to be applied multiple times a year.

You may not want to use straw or hay from ryegrass as it has toxins in it, and definitely not from grass that has been sprayed with pesticides such as Roundup, which is common in many countries. The difference between straw and hay is that hay has many more seeds, so it will often actually produce weeds.

4. Grass clippings are not the best mulch to use in organic gardening because they get so tightly packed together that they inhibit air circulation. Besides, they are far too important for the soil of your lawn to bring into the garden. They do not contribute to thatch or any other lawn problems, but they provide many benefits so they must be left there. If you have extra though, a tiny amount could be used as a part of your mulch.

5. We're getting closer to our my favorite of all mulch types, but not yet. With all this talk about organic matter, why not just use compost? A little bit of thought tells us why. It does a lot of things right, but fails to stop the weeds! The same goes with manure, and manure needs to be composted before applied to soil anyway. We should use compost and manure, but they are not really the best mulch. I cover compost in detail in the Smiling Gardener Academy along with cover crops because they are both excellent ways to increase the organic matter content of the soil, but here, we're looking for the best mulch.

The Best Mulch Types

What is mulch, I mean the best mulch - what is it? It's organic matter and it's provided by nature. In a well-designed organic garden, this is one of the only types of mulch that magically appears in our beds in autumn, protecting the soil over winter, and breaking down throughout the following spring and summer until a new batch magically appears in autumn.

Number 1

Of all the mulch types, by far the best for organic gardening is: leaves! They do absolutely everything right. That's why when we're designing our gardens we want to make sure to use plants that make a lot of leaves - not just evergreens - and we want to design the beds to catch all of these leaves.

Leaves are by far the best mulch type

Those that fall on the lawn and non-garden surfaces can be raked into the gardens or mulched right on the lawn.

If you don't have enough leaves, your neighbors will usually be happy to give you theirs, since they would otherwise have to rake them up and dispose of them. In many cities, you can rake your leaves to the curb and a big truck will come by to pick them up. But why would you want to give the best mulch ever away unless you have too many?

Ironically, some organic gardeners do this and then buy the leaves back as leaf mould in the spring. Leaf mould is just leaves that have been slightly decomposed. Leaf mould is one of the best mulch types, too, but in most cases, the gardener would have done much better to save the money and keep the leaves in the garden over winter where they can protect the soil.

If you have a thick enough layer of leaves in your garden (2" to 4" is nice), many weeds will be smothered. You will still get some weeds, but they will be so easy to pull that it won't matter. You can just drop them back on top of the leaves to become part of the best mulch ever.

Some people think leaves are not one of the most attractive types of mulch for the garden, but is a forest floor unattractive? Or is the forest floor covered in 2 inches of bark?

We’ve been conditioned to think that bark mulch or bare soil is the most aesthetically pleasing, but if you covered your organic garden in a rainbow of autumn leaves, I think you’ll see it differently, especially now that you know all the benefits they provide.

When we remove the leaves, we are breaking nature's cycle and creating more work for ourselves.

So leaves are the number one best mulch.

Number 2

There is one other organic gardening material that doesn't take the place of leaves as the ultimate of all the types of mulch, but it is beneficial to have as well. It's called a living mulch, i.e. plants. A living mulch is a dense plant cover on the soil, especially low growing "cover" crops.

These can be annual crops (also known as green manures) that we plant in our vegetable gardens to protect the soil during certain times of year and to provide organic matter to the soil, or perennial plants (also known as groundcovers) that live permanently in our ornamental gardens underneath our flowers, shrubs and trees.

A good goal is to make sure all of your soil is consistently covered with plants, and cover crops help achieve this goal. Plants send out hormones in the vicinity of their roots that tell weed seeds not to grow.

As long as your organic garden is dense with plants and leaves (the best mulch ever), and your lawn is dense with healthy grass, those weed seeds will mostly stay dormant and you have a whole list of other benefits to which you can look forward.

Mulching All Your Leaves - There Are Exceptions

It is possible to have too many leaves if you have a lot of big trees or if your beds are already covered in groundcovers and you don't want to totally smother them.

In that case, you may just have to compost them or give some away, to a friend or to the city, although I have mulched 12 inches of leaves into some lawns with great success.

Actually, when I was a kid, I recall my dad would pile a bunch of leaves in the back of the pickup truck (we lived in the country), head down the street to where there were no houses, drop the tailgate, and hit the gas. It was so much fun watching the leaves get caught by the wind and cover the sky like a thousand red and yellow butterflies. In hindsight, I have no idea why we did this, but it was fun at the time.

I know someone reading this is wondering about oak leaves. I've never had a problem with the fact that oak leaves don't break down quickly. I've always enjoyed that about them because it just means my mulch stays around longer. And nope, they don't acidify the soil. But again, if you have too many, don't force it.